Discusses blood test to check level of potassium (K) in blood. Includes info on what affects potassium levels in the body such as kidney function, blood pH, and hormones. Explains how and why test is done. Covers what results mean.

Potassium (K) in Blood

Test Overview

A
potassium test checks how much potassium is in the blood. Potassium is both an
electrolyte and a mineral. It helps keep the water
(the amount of fluid inside and outside the body's cells) and electrolyte
balance of the body. Potassium is also important in how nerves and muscles
work.

Potassium levels often change with sodium levels. When
sodium levels go up, potassium levels go down, and when sodium levels go down,
potassium levels go up. Potassium levels are also affected by a hormone called
aldosterone, which is made by the
adrenal glands.

Potassium levels can be
affected by how the
kidneys are working, the blood
pH, the amount of potassium you eat, the
hormone levels in your body, severe vomiting, and
taking certain medicines, such as
diuretics and potassium supplements. Certain cancer
treatments that destroy cancer cells can also make potassium levels
high.

Many foods are rich in potassium, including scallops,
potatoes, figs, bananas, prune juice, orange juice, and squash. A balanced diet
has enough potassium for the body's needs. But if your potassium levels get low, it can take some time for your body to start holding on to potassium. In the meantime, potassium is still passed in the urine, so you may end up with very low levels of potassium in your body, which can be dangerous.

A potassium level that is too high or too low can be
serious. Abnormal potassium levels may cause symptoms such as muscle cramps or
weakness, nausea, diarrhea, frequent urination,
dehydration, low blood pressure, confusion,
irritability, paralysis, and changes in heart rhythm.

Other
electrolytes, such as sodium, calcium, chloride, magnesium, and phosphate, may
be checked in a blood sample at the same time as a blood test for
potassium.

Check to see whether certain cancer treatments are causing
too many cells to be destroyed (cell lysis). Cell lysis syndrome causes very
high levels of some electrolytes, including potassium.

How To Prepare

You do not need to do anything before
having this test.

Talk to your doctor about any
concerns you have regarding the need for the test, its risks, how it will be
done, or what the results will mean. To help you understand the importance of
this test, fill out the
medical test information form(What is a PDF document?).

How It Is Done

The health professional drawing blood
will:

Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.

Clean the needle site with
alcohol.

Put the needle into the vein. More than one needle stick
may be needed.

Attach a tube to the needle to fill it with
blood.

Remove the band from your arm when enough blood is
collected.

Put a gauze pad or cotton ball over the needle site as
the needle is removed.

Put pressure on the site and then put on a
bandage.

How It Feels

The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch.

Risks

There is very little chance of a problem from
having blood sample taken from a vein.

You may get a small bruise at the site. You can
lower the chance of bruising by keeping pressure on the site for several
minutes.

In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.

Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (such as Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.

Results

A potassium test checks how much
potassium is in the blood. Potassium is an
electrolyte and mineral.

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Many conditions can affect potassium levels. Your doctor
will talk with you about any abnormal results that may be related to your
symptoms and past health.

High values

High blood potassium levels may be caused by
damage or injury to the kidneys. This prevents the kidneys from removing
potassium from the blood normally.

High blood potassium levels can
also be caused by conditions that move potassium from the body's cells into the
blood. These conditions include severe burns, crushing injuries,
heart attack, and
diabetic ketoacidosis.

Taking too many
potassium supplements can also cause high levels of potassium in the
blood.

Too much acid (pH) in the
blood makes potassium levels higher by causing the potassium in the body's
cells to "leak" out of cells and into the blood.

Some medicines,
such as aldosterone antagonists and angiotensin-converting enzyme (ACE) inhibitors, can cause high
potassium levels.

Low values

Low blood potassium levels can be caused by
high levels of aldosterone (hyperaldosteronism) made by the
adrenal glands.

Other conditions that can
cause low blood potassium levels include severe burns,
cystic fibrosis, alcoholism,
Cushing's syndrome, dehydration, malnutrition,
vomiting, diarrhea and certain kidney diseases, such as Bartter's syndrome.
Bartter's syndrome is a condition characterized by enlargement of certain
kidney cells. It is more common in children and may be linked to an
abnormally short stature (dwarfism). The cause of Bartter's syndrome is not
fully known.

Medicines, such as
diuretics, are a common cause of low potassium
levels.

What Affects the Test

Reasons you may not be able to
have the test or why the results may not be helpful include:

Destruction of the red blood cells in the blood sample, which can happen when blood is taken or when it is being processed in the lab. When red blood cells are broken up, they release large amounts of potassium and can cause false high values.

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